Process of making nitric acid



par

i If

TATE

FICE.

JAMES H.

LOW'.

SHAPLEIGI-l, F MOUNTAIN LAKES, -NEW' JERSEY, AND CHARLES A. BIGE- 0F WILMINGTON, DELAWARE, ASSIGNORS TO HERCULES POWDER' COM- PANY, OFW'ILMINGTON, DELAWARE, A. CORPORATION OF DELAWARE.

PROCESS OF MAKING NITRIC ACID.

The object of our invention is to provide a. nenmethod of manufacturing nitric acid. In our specified and preferred process, which comprises features all of which are of advantage and importance, out not all of Which are essential to the successful execution of the process, there are continuously fed to one end of an elongated retort about equal quantities of sodium sulfate and sodium nitrate and the amount of sulfuric acid required to react. with the sodium nii I trate to form nitric acid gases andconvert thev sodium nitrate to sodium sulfate with no, or a `minimum.' production of sodium acid sulfate. The retort is so differentially heated that the material relatively near the feed end of the retort 'Will be subjected to a relatively low heat with resultant production of a maximum proportion of gases yielding, on condensation, strong nitric acid, While the material relatively near the discharge end of the retort will be subjected to the relatively high heat required to complete the reaction of sulfuric acid and sodium nitrate, with resultant production of gases (largely oxides of nitrogen from decomposition due to high temperature) adapted, on condensation7 to yield Weak strength nitric acid. The different evolved 0 gases are preferably separately Withdrawn from the retort and separately condensed and absorbed. inasmuch as the different gases are evolved in single retort, the proportions oi different. gases that are separately 5 withdrawn may be regulated hy applying suction at the separate gas outlets and varying the suction. The originally introduced sodium sulfate n acid and the sodium nitrate (which, if the process is carefully conducted', will comprise mainly or Wholly normal sodium sulfate) are continuously discharged from the retort, and a part of this discharged material (about i one-half) is conveyed hack to the feed end of the retort and is used as the source of supply ofthe sodium sulfate vwhich, together with the sodium nitrate, is continuously fed int-o the retort. The retort is preferably l heated by means of hot gases that are first brought into heat exchange relation with the retort at its discharge end and which nitrate.

and the non-gaseous prodnets of the reaction between vthe sulfurle' Application tiled August 5, i925. Serial No. 48,216.

flow along the retort in a direction opposite to the direction of movement of the salts in the retort; more or less of the heating gases being lay-passed duringtheir ow along the retort so as to provide heat zones in the retort of substantially different tem peratures, as above stated. The salts entering the retort should be reheated, and the Waste heating gases may he utilized for this purpose. However, if, as above described, the sodium sulfate discharged from the retort be utilized as the source of supply of the sodium sulfate Which is continuously being fed to the retort, such sodium sulfate may he utilized to preheat the sodium nitrate with which it is mixed before entering to the retort', and the Waste heating gases may therefore be used to supply any additional heat which it may be desirable or necessary to impart to the entering sodium The salts that travel through the retort should be agitated so as to maintain them in mixed condition and establish the most favorable conditions for reaction 'loetiveen the sodium nitrate and the sulfuric aci Different apparati may be employed to carry out our process. lVhile, therefore, it should be understood that the successful execution of the process is not dependent on the employment of any panticular'apparatus, we herein disclose an apparatus whichv is -well adapted to carry on the process with a high degree of eticiency and economy.

In the drawings:

Fig. l is a4 diagrammatic vievy, in sectional elevation, of such an apparatus.

Fig. 2 is a cross-section on the line 2-2 of Fig. l, also diagrammatic.

Through a brick setting a extends a rotatable cylinder b Which serves as a retort. The retort isprovided with a drive gear 0 which is driven from driving means not shown. Within the retort are angle plates d or other means for imparting additional agitation to the contents of the retort dur ingr its revolution. The retort is provided with rings e which revolve on trunnions .f with Water cooled bearings Within the setting a. The 4retort may be inclined somewhat to the horizontal to effect a forward feed of the material, and internal contrvd *so "ne abone twenty feet in ngt?! and abone ve feet in iemeer, is; led, to a depth of about afoot or so, W'rh dry sodium suae, Say, o example, 4G00 1Lgoundsn The ice is ei'zuteda he'ore of after endne', and die ue dempers are adjusted so as to produce the desired reacon tempera-tures in different zones of the etort. Fol example, the retort. may be so dfeentielgs' heeed 'la, the charge adjacent the feed en of l*the feiert wm be at approximately 300"V F. while the charge in succeeding Zones Wl be hea'ed io progressvey higher temperatures, until, in the inal zone. the chalge will be hemed to n eempemture of approxmaey 3500 F. These examples me merely preferential. The possible extreme range of temperature ef the c'le'ge would be pobaby from substentialy Cold at the feed en t almost any temperature short of the melting "point of sodium sulfate at the discharge end.

lo along my er all. oi "me gas may he i thm; M ei? eine, eommmuce The number of heat zones and the tempereures in the several Zones are matters for C e emmon by those prractfng the process. T? 4se aetoe may vmy with the stfengh of desied to be produeeds the amount of in he reior at any one time, the .fate Y,ed ofsale and sulfuric aed into 'the re- .e umg, tow; the lengh of the-etort, the temperature f 3 3" Z'EGRPS o? Joe matefe when it enters the, eort and,

man those cesebe, length of time reoued for the 'materiel n imm of the emmene end of -e reo' no reverse the retort. L in the exemple which eoaum 'einem enf fdl the beppe? sodium nitate, are. contnuousy feci into 'the feoct the rate of about 500 pounds of each Sali. per hour. The salgas are preferaby Hofe en n, i o'he retot and they 1 'ay pi vheatei: by means hereeeserbed, io any euiabe tempera" *2:1* efiample e tepelature approxiim@ empemtue n the flst zone of retort, eo that lmmedlae leaotlon "vided with a y. From this suele?, @oeufs Within le eto': when the acid Comes r' oamrymg www the in diaet Wim the nime. Sulurc ecd is i, one. o1* *dus me Smeg-fed luto he retortg near its feed end, at

7 l he o about 288 pounds pef Dour and l m :floh marmer ahah it is dmcmbuted m the einfgffl, be convoy, afi the www feed pm "Rime, This amount of sufuio acid epeeef s about that heoreoay Tequre to z'eeet 'with Foe speced amount of som m Tie to produce ntxic acid and normal sedi; n

l @e115 sodium sulfate.

therein. 'me VSmee the eo-lum mate 1s i'mfgmiy et a. fw bemeen 'one le goed fenaison Lempereture, mime amd raie 'winch the nre aoc ges is viven eoreases, the progressvey higher te2- zones offset Ier ey the Tate ve. Furi-her; che smlium Sulfate cs inem M167 together wiih H'le quo-z refute? ehe mees in e. reetvejy ry more ieee' 'free em baing, a nzi'ee of eoxm is given o rapidly et he siert. A5 they Lil and quality.

' material to traverse the retort -of sulfuric acidv` as in complete the product.

:tls the mixture nears the end zone, or hot- 3 test zone.

I the reaction is relatively complete the sodium nitrate is converted ,to norma sodium sulfate, and normal sodium sulfate is discharged jlroin the retort. A part ot thevv discharged material. ior example, one hall', is returned to the l'ecd end ot' the retort and serves, through its 'heat content, to economically heat the ingoing sodiuru nitrate. As hereinhet'oie stated, Waste heat troni the line gas is also available to supplement the heating action ot' the sodiutn sultats.

Assuming that the initial char e of material is about 4000 pounds, that tiis amount of material isiinaintained in the retort, and thatthe material is t'ed into the retort at the rate specified, the length of time required for will be about four hours.

The hull: of the reaction takes place near the feed end arid at relatively lon' temperatures, givingl a high percentage o' strong acid. Further toward the discharge end, and under the higher temperature conditions. required to complete the reaction or sodiuni nitrate to sodium sulfate, the nitricacid dissociates, prod peak strength acid.

All-the nitric ucid may he taken from a single exit, hut `this is highly inadvisahle,

and therefore separate gasexit lines u and fu,-

are provided near or at the feed end and clischarge end respectively. Thereby mixing ci nitric acid gases of Widely7 ditlerent temperatures is avoided. lhc number of gas exit lines and their locatibn are matters for the judgment of those operating the apparatus. By applying suction to the gas exit iues and controlling the relative amounts of suction in the tivo llues, the amount of gas delivered at each end ,may be accurately controlled.

from the foregoing description it will he understood that by regulating the factors of rate of feed, temperature, etc., nitric acid may he continuously distilled with directproduction, as a hy-product,'of normal sodium eslfate (which has Aa substantial Inarlret value) in contrast to the production, as in the usual process, of sodium acid sulfate (a. product rit-low value), and. Without Waste llrcu it the process the highest' skill or under the best conditions, .so that some acid .sodium sulfate may be formed, the process presents advantages with respect to-economy and continuity.

Due to the Zones of progressively increasing and readily controllable temperature, the nitric acid produced is or" desirable strength The use ot' sodiuin sulfate in the reaction mixture 1s a factor that materially contributes to the success of the process.

enanas the usual proccss.` he not carried out with.

i The' utilization ot unete heat and of the heat ot the discharging and re-used sodium sulfate make the fuel economy high.

After the process has continued for a short time, and' it the desired differential temperavture coiulitions are maintained, the conditions within llic retort remain lined. The proportion of sodium sulfate in the retort is maintained at trom about filly per cent at the feed end to one hundred per cent at the ilischarge cud. At' any given point along the length ol' the retort, the composition ot the mixture (amount and proportion of each salt), the temperature, and the gus composition remain unchanged. Once started, therei'orc. the operation requires a` inininiun'i of labor.

There is. of course` heat transfer from one zone ot' the retort to another, the effect of which. however, if the dainpers are properly miljusted, is not to create, within the retort, a uniform temperature, but a gradual increase of temperature from one zone to the next.. ln other words. instead of distinct zones of diii'erent tcnuieratures, there is a more ory less gradual increase of temperature from one zone to another, which is a condition more 1Ir'avorable to an economical and ecient practice of the process than distinct zones with abrupt temperature rises from one to another. r

Over the batch process that is in use. our process has distinct advantages other .than those hereinbefore pointed out. .lt is devoid ot critical points such as primes andv hence does not require nursing, like the hatch system. The latter requires very careful heat regulation and an experienced renian for pushing and holding the lires, whereas in our process the temperature conditions, once properly adjusted, need only he maintained constant. The alternate heating and cooling` of the hatch system is a serious source of heat vvaste. Not only does our process avoid this waste of heat, but. the residual heat of the flue gases and thc absorbed heat of the discharging sodium sulfate are hoth availed of 'to preheat the entering salts. i

By reason of the continuity of the process, great economy nuiy he attained in the inst-allation Ifof condenscrs and towers for handling theniitric acid. I

While We have described` and hereinafter claim` the continuous feeding of salts and sulfuric acid into the retort and the continuous discharge therefrom of sodium sulfato. and while ahsolute continuity is contenu'iluted vvhere it can he convenientlyinaintained, We do not nie-an to to absolute continuity as distinguished from such substantiel continuity as would be afforded hy intermittent admission and discnarge, hut intend, in referring to the process as continuous, to exclude hatch treat- N general liinit the process llt) lill) ments and such substantial departures from literal continuity as would nidintain substan tially variable, as distinguished from substantially fixed and constant, conditions in the retort.

While we prefer to vfeedainto the retort about equal quantities of the two salts, and while the feed of sodium nitrate and the feed of sulfuric acid should he so proportioned as to insure the conversion of the highest ossihle proportion of sodium nitrate to nitric acid and sodium sulfate, the proportions of sulfate relative to nitrate that should he fed into the retort he varied from that specified Within rather ivideflimits. v

Having now full y described our invention, `vvhat ive claim and desire to protect by Letters Patent is:

l. The process oi making nitric acid which comprises continuously feeding` sodium niu trate, normal sodium sulfate and uncomhined sulfuric acid to and along a confined path, subjecting said salts during their travel along said path toagitation and to differential heating varying from a relatively low temperature relatively near the .feed end of thepath to a relatively high ternperature relatively near the discharge end of said path, continuously discharging from said confined path the sodium sulfate admitted thereto and the sodium sulfate produced hy the reaction of the sulfuric acid with the sodium nitrate, the proportion of sulfuric acid Jfed to Said path being not substantially in excess of the proportion theoretically required to produce nitric acid and normal sodium sulfate and the proportion of normal sodium sulfate fed to saidvpath being sufficient to provide the conditions required to prevent conversion of substantial amounts of sodium sulfate to sodium acid sulfate, and controlling said temperature to produce, hy the reaction of the sulfuric acid with the sodium nitrate, gases, relatively near the feed end of the path, adapted to yield on condensation relatively strong; nitric acid and gases, relatively near the discharge end ot the path, adapted to yield on condc-nsation relatively low strength nitric acid.

2. The process defined in claim l comprising also the utilizaton of the discharged salt as a source of supply of the sodium sulate that is ied to said confined path.

The process of' making nitric acid which comprises continuously feeding sodium nitrate, normal sodium sulfate and uncomoined sulfuric acid to and along a confined path, subject-ing said salts during their travel along said path to agitation and to differential heating varying from aV relatively lovv temperature relatively near the feed end o the path to a relatively high temperature relatively near the discharge end of said path, continuously discharging from on condensation relatively i'ovv strength nitric acid, and utilizing hot gas-.es from e. sin gie source to vsupply heat tothe materie said confined path, conveying` c; per said hot gases into heat ancha-nge :i with said material and vhy bypassing o t mainder, a predominant proportion the rstnamed portion of gases' being conveyed int-o heat exchange' lrelation with the materiall relatively nearthe dischargeend et said at i. i p 4. The process of .making nitric acid which comprises continuously feeding sodium nitrate, normal sodium sulfate and uncombined sulfuric acid to and along a ccnined path, subjecting said salts durin their travel along said path to agitation an to dieren#y tial heating varying trom a relatively low temperature relatively near the feed 'endv of the' path to a relatively high temperature relatively near the discharge end ot said path, continuously discharging from said conined path the sodium sulfate admitted thereto and the sulfate produced hy the reaction ci? the sulfuric acid with the sodium nitrate, controlling said temperatures to produce, hy the reaction of the sulfuric acid with the sodium nitrate, gases, relatively near the iced end of the path, adapted to yield on condensation relatively strong nitric acid and gases, relatively near the discharge end of the path, adapted to yield on condensation relatively low strength nitric acid, and separately withdrawing gases produced relatively near the feed. end of said path and gases produced relatively near the discharge end of said path.

5. The process defined in claim' i comprising also the regulation of the relative preportions of the separately Withdrawn gases by applying suction to the outlets and controlling the degrees of suction.

in testimony of which invention, We have hereunto set our hands at Philadelphia, Penna., on this 29th day of July, i925.

.rai/ms i-r. Sennheiser. CHARLES A. Brennen. 

